1. Field of the Invention
The invention relates to an electronic control unit and more particularly, to the structure of a pad portion for connecting a connector and a circuit substrate of the electronic control unit by wire bonding.
2. Description of the Related Art
Hitherto, a circuit substrate constituting an electronic control unit is generally contained in a resin case (b) which is formed integrally with a connector (a) as shown in FIG. 8, and the circuit substrate (c) is electrically coupled to the connector (a) through a number of strip-like terminal plates (e) which have been molded integrally with the resin case (b) by die molding. Each of the terminal plates (e) has one end formed as a pin projecting into the connector (a) and the other end formed as a lead portion (f) having a face exposed at the pad portion (d) which is formed in the case (b). The lead portions (f) which are arrayed close together on a common plane in the pad portion (d) are designed to terminate at the front face of the pad portion (d).
The terminals at the side of the circuit substrate (c) are respectively connected to the lead portions (f) at the side of the terminal plate (e) by wire bonding which has been increasingly employed because of easy processing. Wire bonding is a method for bonding metals by compressing and vibrating an end of the bonding wire (g) formed of aluminum or the like to the lead portion (f) of the terminal plate e), with a bonding tool and using high frequency vibration, so as to remove soil or oxide film from the press fit portion.
Referring to FIG. 9, the lead portion (f) of the terminal plate (e) is fixed within the resin molding (case b) with its upper surface exposed to allow bonding to the wire (g) and has a thin embedded thickness. Therefore it is difficult to provide sufficient strength in the bond between the case (b) and the pad portion (d). More importantly, because the tip of the lead portion (f) terminates at the front face of the pad portion (d), in a so-called open state, sufficient force to arrest the movement of the terminal plate (e) cannot be obtained.
As described above, in the related art, the terminal plate (e) is held in place merely at a short portion of its length where it passes through the wall of the case (b). Accordingly, if the wire (g) is pressed against the lead portion (f) in the pad portion (d), using the bonding tool to apply vibration for effecting the wire bonding, the lead portion (f) which is insufficiently fixed is also vibrated together with the wire g), thus inhibiting formation of a good bond between the wire (g) and the lead portion (f).